450
7 Applications: Pebble Flow Optimizations
Fig. 7.6 Changing R stag within 150 s simulations
A detailed description of the changing R stag of different wall configurations is
shown in Fig. 7.6. Each line is labeled like “shape_radial dimension (mm)_interval
(cm)” to help to distinguish different pebble beds. This method of expression is also
utilized in the following figures.
In Fig. 7.6, the first 50 s of the simulation are not displayed because all the lines
representing R stag in different beds coincide with each other and do not split until
reaching about 65 s. In all the beds, pebbles drained out before 65s completely belong
to initially loaded pebbles. It takes a while for newly loaded pebbles to flow down
from the top to the discharging hole. This is why all the R stag profiles decline linearly
at the same rate depending on the circulating rate (40 pebbles per second) before a
certain time point.
The stagnant rate, R stag , that decreases rapidly and reaches 0 is the best and most
expected result. This can ensure the elimination of stagnant regions and consistent
flow in the pebble bed, which lowers the risk of reactor accidents. According to Fig.
7.6, at 150 s, all the beds with wall structures achieve lower stagnant rates than a
normal bed.
In this figure, “triangle_12_20” is the best option among the investigated configurations since it reaches the lowest value for R stag at appropriately 5%. It is
noted that only “triangle_12_20” and “triangle_12_10” successfully reduce R stag
to below 10% within 150s. Therefore, it can be said that the beds with triangular
wall structures generally have better performance over the beds with arcs and sawteeth in prohibiting stagnant pebbles. Besides, by comparing “triangle_12_20” with
“triangle_12_10” and “arc_12_10” with “arc_12_20”, a relatively larger interval
(20cm, about 16.7 times of pebble diameter) works better. The reason is that the
influence of wall structures is twofold: the structures can definitely prevent crystallization along the walls. However, they would increase the resistance of the pebble
7 Applications: Pebble Flow Optimizations
Fig. 7.6 Changing R stag within 150 s simulations
A detailed description of the changing R stag of different wall configurations is
shown in Fig. 7.6. Each line is labeled like “shape_radial dimension (mm)_interval
(cm)” to help to distinguish different pebble beds. This method of expression is also
utilized in the following figures.
In Fig. 7.6, the first 50 s of the simulation are not displayed because all the lines
representing R stag in different beds coincide with each other and do not split until
reaching about 65 s. In all the beds, pebbles drained out before 65s completely belong
to initially loaded pebbles. It takes a while for newly loaded pebbles to flow down
from the top to the discharging hole. This is why all the R stag profiles decline linearly
at the same rate depending on the circulating rate (40 pebbles per second) before a
certain time point.
The stagnant rate, R stag , that decreases rapidly and reaches 0 is the best and most
expected result. This can ensure the elimination of stagnant regions and consistent
flow in the pebble bed, which lowers the risk of reactor accidents. According to Fig.
7.6, at 150 s, all the beds with wall structures achieve lower stagnant rates than a
normal bed.
In this figure, “triangle_12_20” is the best option among the investigated configurations since it reaches the lowest value for R stag at appropriately 5%. It is
noted that only “triangle_12_20” and “triangle_12_10” successfully reduce R stag
to below 10% within 150s. Therefore, it can be said that the beds with triangular
wall structures generally have better performance over the beds with arcs and sawteeth in prohibiting stagnant pebbles. Besides, by comparing “triangle_12_20” with
“triangle_12_10” and “arc_12_10” with “arc_12_20”, a relatively larger interval
(20cm, about 16.7 times of pebble diameter) works better. The reason is that the
influence of wall structures is twofold: the structures can definitely prevent crystallization along the walls. However, they would increase the resistance of the pebble